Game and Watch
Game and Watch started the handheld era of games and is the predecessor of the gameboy. Gunpei Yokoi. He came up with an idea for a watch that doubled as a
mini-game to pass the time at work, home, school, etc., and thus the Game and Watch was born. There are 59 Game and Watch games that were in stores, most famous including the first G&W game, "Ball", arcade ports including "Donkey Kong", "Donkey Kong Jr.", and exclusive G&W games like "Octopus". The 'Game and Watch Gallery' series featured classic G&W games for Gameboy, and was later released to the Gameboy.
mini-game to pass the time at work, home, school, etc., and thus the Game and Watch was born. There are 59 Game and Watch games that were in stores, most famous including the first G&W game, "Ball", arcade ports including "Donkey Kong", "Donkey Kong Jr.", and exclusive G&W games like "Octopus". The 'Game and Watch Gallery' series featured classic G&W games for Gameboy, and was later released to the Gameboy.
Game Boy (1989, DMG-01)
In the age of LCD Games being the only real way to play games on the go, the Gameboy must have seemed like a dream that had just come true to gamers. It had an LCD Dot Matrix screen that allowed more than one game to be played on it through interchangable cartridges you could buy. Before Gameboy, LCD games made up the portable game market, and they weren't impressive. Gameboy changed this and changed portable gaming forever. It seemed almost every popular NES game had been ported to Gameboy as a port or even a sequel to an NES title, such as with Contra and Metriod, making it feel like a portable NES, and it had a huge library of unique games.
Game Boy Pocket
Released in 1996, the Gameboy Pocket was a smaller version of the original Game Boy. It also had a sharper, larger, less tinted screen, and was the first and only Gameboy to use 'AAA' batteries. It came in the same colors as the 'Play it Loud' series, a series of Original Gameboys that came in multiple different colors released in 1995. It took out the lock-out bit of plastic on the original Gameboy, so you can get GBC carts inside it, though most if not all just give you an error message.
Game Boy Color
In 1998, the Gameboy Color was released. It sported a very sharp full color screen with a unique shape for a more comfortable grip. It came in 5 colors upon release, the same colors found on the word 'COLOR' in the logo; Red, Blue, Lime Green, Yellow, and Purple. Another Color (Transparent Purple) and Special Pikachu Edition were released later. Most of its library consists of ports of N64 games, as well as a good amount of original games. It included full support for original Gameboy games.
Game Boy Advance
Released in 2000, the GBA revolusionized portable gaming at the time. With a new 3D graphics processor and upgraded graphics from previous Gameboys, the GBA was a massive success, and would even be redesigned twice. It had a library of Gamecube game ports and unique games similar to the GBC.
Game Boy Advance SP
Released in 2002, then re-released in 2003 with a more vibrant colored screen, the GBA SP did almost as well, if not better than the original GBA. Sporting a new backlight for playing out of direct sunlight or at night, a rechargable battery, and a unique flip-phone styled design, it set the stage for Nintendo's DS system that came a few years later.
Game Boy Micro
Even though It didn't sell incredibly well (you can tell Nintendo put a lot of money into the GBM, from interchangable faceplate concept to the commercials, only to have it flop), the Micro did improve on the GBA SP's already impressive backlit screen as well as fit the GBA into a smaller casing and added a bit of customization to it by allowing interchangable faceplates. It was unfortunatley released after the DS dominated the handheld market, leaving the highly underrated GBA Micro to die, and as a result, it was the last Game Boy made. There was also a Famicom 20th Anniversary version released, but you couldn't take the faceplate off it.